1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet performance maintaining device for effective use in a color ink jet recording device which includes a plurality of recording heads.
2. Discussion of the Related Art
An ink jet recording apparatus normally includes an ink jet performance maintaining device which is used to maintain the ink jet performance of the recording apparatus.
The jet performance maintaining device, by covering the nozzle surfaces of recording heads with their caps when not in printing, restricts evaporation of ink volatile material from the nozzle portions of the recording heads when not in printing, prevents printing troubles caused by the failure to jet ink due to the increased ink viscosity, and effectively prevents dust floating in the air from attaching to the nozzle jet surfaces.
Further, the jet performance maintaining device of this type, after a recording head or an ink tank is replaced with a new one, initially fills the new recording head or ink tank with ink, or, in the maintenance thereof, removes thickening ink, dust, air bubbles and the like filled in the nozzle of the recording head so as to be able to restore the ink jet performance thereof. Also, the jet performance maintaining device includes, besides the caps for covering the nozzle surfaces of the recording heads, a negative pressure suction pump connected in communication with the caps and an exhaust ink tank connected in communication with the negative suction pump, whereby the thickening ink and the like existing in the recording heads can be sucked and collected through the caps.
A color ink jet recording apparatus, in fact, requires a plurality of recording heads respectively used to jet their corresponding color components of ink, and therefore, the jet performance maintaining device must include a plurality of caps respectively corresponding to the recording heads, and also must be able to exert a negative pressure suction force, with the recording heads being covered (that is, capped) with their corresponding caps so as to perform a jet performance recovery processing.
In this case, in a system which uses negative pressure suction pumps corresponding in number to the caps, there arises such a fundamental technical problem that the jet performance maintaining device itself is complicated. For this reason, there can be expected a system in which a single negative pressure suction pump is used in common and is connected with the respective caps via a communication tube, thereby being able to simplify the structure of the jet performance maintaining device.
However, if a jet performance recovery processing is performed in the above system, then the ink contained in all of the recording heads is sucked and collected at the same time. In other words, even when the jet performance recovery processing is to be executed only on the recording head for jetting black ink, the ink from the recording heads for jetting other color ink than the black ink will also be sucked and collected wastefully.
To solve the above problem, there has been already provided a system which additionally includes on its negative pressure suction pump side a communication system selector used to switch the communication systems of the respective caps (Japanese Patent Unexamined Publication No. Hei 2-1325).
However, in the system of the above-mentioned type, the additional provision of the communication system selector complicates the structure of the negative pressure suction pump. Further, since the negative pressure suction pump and ink suction passages respectively in communication with the caps must be switched and selected, there arises such a technical problem that it is difficult to secure the airtightness of the ink suction passages.
Also, it is true that the addition of the communication system selector makes it possible to selectively perform a jet performance recovery processing on one of the recording heads but, for example, when the jet performance recovery processing is to be performed on all recording heads, the jet performance recovery processing must be sequentially executed on the recording heads one by one, which produces a new technical problem that the time necessary to perform the jet performance recovery processing is increased.
Further, while the recording heads are not in printing, if there is executed a capping operation to close tightly the nozzle surfaces of the recording heads with the corresponding caps, then the volumes of the caps are decreased only slightly with the elastic deformation of the respective caps. This raises a problem that a very slight positive pressure will be inevitably applied to the nozzle surfaces of the recording heads, which may move back the ink existing in the nozzles.
At that time, since the recording head is kept in a state where ink is not filled in the nozzle, when the capping operation is released and a recording head printing operation is executed, there is a possibility of producing a printing failure that the ink cannot be jetted surely.